1. Field of the Invention
This invention relates to improvements in quantitative analysis instruments utilizing a plurality of radiation emitting diodes such as IREDs and particularly to an optical arrangement for such instruments to assure that the energy distribution on the test samples is the same from each of the IREDs.
2. Description of the Prior Art
There are known in the prior art instruments for quantitative analysis utilizing near infrared radiation energy. These instruments can measure chemical constituents in a sample by either reflecting the radiant energy off the product or transmitting it through the product. Such instruments utilize a phenomenon that certain organic substances absorb energy in particular portions of the spectrum. By measuring the amount of energy absorbed by the sample at certain specific wavelengths, precise quantitative measurements of the constituents in the sample can be determined. For example, the measurement of protein content in wheat can be performed in this manner. For a general introduction to near infrared quantitative analysis, see the paper presented by Robert D. Rosenthal to the 1977 Annual Meeting of American Association of Cereal Chemists entitled "An Introduction to Near Infrared Quantitative Analysis".
In prior application, Ser. No. 73,965 filed Sept. 10, 1979 there is disclosed an apparatus for near infrared quantitative analysis utilizing pulsed infrared emitting diodes (IREDs). Reference may be had to this application for further prior art and background information.
When utilizing multiple IREDs in a near infrared quantitative analysis instrument it is desirable to mount them in a geometric array or a matrix. However, because each IRED does not emit parallel light the radiation falling on the sample may vary from IRED to IRED thus creating a variation in the readings from the instrument. Attempts to correct these problems can involve expensive optical elements. Thus, there is need in the art for the use of low-cost simple elements that can provide identical accuracy, precision and energy distribution on the sample. This need arises from the technical problem in that the individual light elements (for example the IREDs) typically have collimating lenses built into them. The purpose of such lenses is to provide a light beam that is as parallel as possible. However, due to practical limitations in optics including atmospheric dissipation the light emitted is never truly parallel and typically emanates at angles up to 8 degrees off of a parallel path. The light exiting from these lenses tends to have large scattering patterns near the focal point and this causes uneven energy distribution on the test samples.